Accurate evaluation of demineralized white spot lesions during orthodontic treatment is important to both clinicians, so they might implement early prevention and/or treatment, and researchers who wish to study the effectiveness of those methods. Assessment will depend on accurate detection and measurement of a lesion, using procedures that demonstrate good validity and reproducibility. A range of evaluative techniques are outlined and the advantages and disadvantages of each are discussed. Some methods can be applied by the busy clinician, whereas others are more suitable for the researcher undertaking a clinical trial. Regardless of who is using the technique, it should be relatively straightforward to apply in the clinical situation, and whatever technique is undertaken, researchers and clinicians must appreciate the need for proper research designs to produce reliable information regarding the effectiveness of any intervention.